Checking Fuel Heater
12-02-2005, 04:24 AM
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Checking Fuel Heater
Last week we had a chilly day, about 18 degrees. I had a two hour drive. About halfway into the drive, the truck started to lose it's "pep" when passing, accelerating, etc. Felt like a clogged filter, I figured I was starting to gel (I was running about b-50 with anti-gel additive).
Stopped and added more anti-gel, topped off the tank (6 gallons is all it would take), and all was well after that. While fueling up, I felt the fuel filter cannister, and it was NOT WARM.
Pretty sure it was just the bio, but, how do I check the prefilter heater? I assume I disconect and test the resistence accross the leads to see if it is operational. Anyone no what the resistence value should be? I assume open means it's bad? Is there a better way to test it?
Also thinking about insulating fuel lines and fuel filter cannister for winter time use. Thanks, Kevin
Stopped and added more anti-gel, topped off the tank (6 gallons is all it would take), and all was well after that. While fueling up, I felt the fuel filter cannister, and it was NOT WARM.
Pretty sure it was just the bio, but, how do I check the prefilter heater? I assume I disconect and test the resistence accross the leads to see if it is operational. Anyone no what the resistence value should be? I assume open means it's bad? Is there a better way to test it?
Also thinking about insulating fuel lines and fuel filter cannister for winter time use. Thanks, Kevin
12-02-2005, 09:41 AM
#2
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There are 2 things to check and that is the heater and the fuel temp sensor.
From my Haynes book the heater element should be approx 1 ohm cold (40°F) and about 1000 ohms warm (80°F). The sensor is a simple open/closed test. Above 40 open, below 40 closed.
Hope that helps.
From my Haynes book the heater element should be approx 1 ohm cold (40°F) and about 1000 ohms warm (80°F). The sensor is a simple open/closed test. Above 40 open, below 40 closed.
Hope that helps.
12-02-2005, 10:46 AM
#3
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Fuel temp sensor is internal to the fuel heater. 12 volt power is always at the heater. Best way to check if the heater is working is to feel if it's warm a few minutes after a cold start. If you want to get more complicated put an amp meter in one of the lines after a cold start.
Wiring to the fuel heater tends to fail but usually is visibly melted.
Wiring to the fuel heater tends to fail but usually is visibly melted.
12-02-2005, 07:04 PM
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Also sounds like it could be your pre screen is getting mucky and the slightest gelling could be causing your troubles, might want to service the pre screen, as it is one of the most overlooked maintnance items on our trucks. Goodluck,,Rick
12-02-2005, 08:46 PM
#5
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On mine, the fuel heater sensor is external, and is screwed on top of the fuel heater assembly. It is replaced at the same time as the harness.
My fuel heater was open, ie, broken, so I got a new heater & sensor at the same time.
My fuel heater was open, ie, broken, so I got a new heater & sensor at the same time.
12-03-2005, 08:22 AM
#6
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Originally Posted by TRCM
On mine, the fuel heater sensor is external, and is screwed on top of the fuel heater assembly. It is replaced at the same time as the harness.
12-03-2005, 11:50 AM
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The sensor actually measures the temp of the aluminum housing at the top of the prefilter/heater assembly right beside the fuel inlet from the tank. My truck has NO other sensors of any kind in the fuel line between then tank and the heater assembly.
As the heater heats the fuel, the housing will also heat up. On mine, there are only two contacts/pins in the connector to the main harness. A sensor internal to the heater puck would require at least 3 contacts/pins. The power to the heater puck itself is routed thru the sensor, so if it isn't cold enough, the puck won't get power to heat.
It is a bimetallic sensor, about the size of a nickle, that has to be in solid contact with the housing to work well. Don't use di-electric grease either, as it will insulate it.
The sensor only comes with the harness, and is around 45 bucks.
As the heater heats the fuel, the housing will also heat up. On mine, there are only two contacts/pins in the connector to the main harness. A sensor internal to the heater puck would require at least 3 contacts/pins. The power to the heater puck itself is routed thru the sensor, so if it isn't cold enough, the puck won't get power to heat.
It is a bimetallic sensor, about the size of a nickle, that has to be in solid contact with the housing to work well. Don't use di-electric grease either, as it will insulate it.
The sensor only comes with the harness, and is around 45 bucks.
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12-03-2005, 12:43 PM
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Well, did a little troubleshooting this morning. Thanks for all the information.
Looks like I have the setup TRCM is describing. The temp sensor has two small torx head screws holding it down to the top of the heater/prefilter housing. Yes, I see where it is all part of a wiring harness that includes the connector for the heat element and the sensor. It appears to be about 18 inches long with a connector at the very end to connect the wires coming from the relay on the firewall.
Well, first thing I found when I removed the 2 pin connector at the heat element was it was wet with diesel fuel. No visable leaking but it was definetly wet on the connector and in the socket that it goes into.
There was no continuity between those two pins (the heating element connection pins). Like mentioned, it should be about 1 ohm when below 40 degrees. I have nothin! So element is toast.
I also checked the temp sensor, and that is operational, or at least I have continuity whith the temp below 40 degrees. The relay also checked out fine.
So, the big question is... does anyone have a source for the new element at a fair price? How about a part number? I have Cummins/Bridgeway in the next town, but they are closed on the weekends and they also moan when I don't have a part number. For the most part they are OK, and they stay open late during the week, but mail order would be fine as well. Thanks again for all the help, Kevin
Looks like I have the setup TRCM is describing. The temp sensor has two small torx head screws holding it down to the top of the heater/prefilter housing. Yes, I see where it is all part of a wiring harness that includes the connector for the heat element and the sensor. It appears to be about 18 inches long with a connector at the very end to connect the wires coming from the relay on the firewall.
Well, first thing I found when I removed the 2 pin connector at the heat element was it was wet with diesel fuel. No visable leaking but it was definetly wet on the connector and in the socket that it goes into.
There was no continuity between those two pins (the heating element connection pins). Like mentioned, it should be about 1 ohm when below 40 degrees. I have nothin! So element is toast.
I also checked the temp sensor, and that is operational, or at least I have continuity whith the temp below 40 degrees. The relay also checked out fine.
So, the big question is... does anyone have a source for the new element at a fair price? How about a part number? I have Cummins/Bridgeway in the next town, but they are closed on the weekends and they also moan when I don't have a part number. For the most part they are OK, and they stay open late during the week, but mail order would be fine as well. Thanks again for all the help, Kevin
12-03-2005, 06:13 PM
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kd460...sounds like you found the same thing I did. I replaced the Harness, but probably didn't need to. I also tested the fuel filter housing with air, and it was leaking bad at the heater connection.
you need to use the part numbers here...the ones infidel posted are outdated.
these are exactly what I ordered and they work great.
thermostat/harness 3943722s $ 49.59
fuel kit (heater & gaskets) 3928013s $ 43.91
these are cummins part numbers I am pretty sure.
I tried to use the ones infidel posted, but they didn't work.
I had the local cummins look them up, then went to a diff diesel shop to get them. they are cheaper, but they get them from the same warehouse the cummins dealer does.
you need to use the part numbers here...the ones infidel posted are outdated.
these are exactly what I ordered and they work great.
thermostat/harness 3943722s $ 49.59
fuel kit (heater & gaskets) 3928013s $ 43.91
these are cummins part numbers I am pretty sure.
I tried to use the ones infidel posted, but they didn't work.
I had the local cummins look them up, then went to a diff diesel shop to get them. they are cheaper, but they get them from the same warehouse the cummins dealer does.
12-03-2005, 09:20 PM
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Infidel's P/Ns are fine. Just depends on the skill of the parts person to get you the most value for your money.
Heater kit 3907766-S
Strainer kit 2845400-S
Both kits get you upper & lower gaskets and less than $40 out the door.
The heater alone is 3928013-S and priced higher than the kit with gasket
Heater kit 3907766-S
Strainer kit 2845400-S
Both kits get you upper & lower gaskets and less than $40 out the door.
The heater alone is 3928013-S and priced higher than the kit with gasket
12-04-2005, 04:34 PM
#12
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well, I used the 3928013s part number, and got the kit, not just the heater.
Also had parts people at 2 diff places look it up and come up with the new numbers, as well as myself at one of the cummins sites.
either way, you should end up with the stuff ya need.
Also had parts people at 2 diff places look it up and come up with the new numbers, as well as myself at one of the cummins sites.
either way, you should end up with the stuff ya need.
12-04-2005, 08:57 PM
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Originally Posted by Burban35
Whats the gain from having your fuel heated?
Diesel fuel is not as winter friendly as gasoline. If you are familiar with winter gel, a functioning fuel heater will extend the temperature range you can straight #2 fuel.
12-05-2005, 04:29 PM
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In my case it helps with running a higher percentage of biodiesel as well. I homebrew, so it is cost effective for me to run as much bio as possible WITHOUT gelling up.
Had limited results finding the part for the fuel heater today. Not in stock at my local supplier, and once again, they had difficulty looking up the part
I posted my frustrations in the "general diesel discussions" category of this forum. Sure would be nice to have a good online source for the parts to our trucks.
They were unable to pull up the part number that tcrm provided, and they did have one listed under the "obsolete" number that infidel provided. So, I ordered it. We will see what shows up from the UPS man. Thanks for all the help, Kevin
Had limited results finding the part for the fuel heater today. Not in stock at my local supplier, and once again, they had difficulty looking up the part
I posted my frustrations in the "general diesel discussions" category of this forum. Sure would be nice to have a good online source for the parts to our trucks.They were unable to pull up the part number that tcrm provided, and they did have one listed under the "obsolete" number that infidel provided. So, I ordered it. We will see what shows up from the UPS man. Thanks for all the help, Kevin